Warm-sensitive afferent splanchnic C-fiber units in vitro

Area of Science:

• Neuroscience
• Physiology
• Sensory Biology

Background:

• The visceral sensory system's role in thermoregulation and cardiovascular control is not fully understood.
• Splanchnic nerve fibers are crucial for relaying information from abdominal organs.
• Understanding thermosensitive afferents is key to explaining physiological responses to temperature changes.

Purpose of the Study:

• To characterize the receptive fields and response properties of warm-sensitive sensory fibers in an in vitro splanchnic nerve-mesentery preparation.
• To investigate the influence of bradykinin and mechanical stimuli on these warm-sensitive units.
• To explore the potential role of these units in cardiovascular responses to heat stress.

Main Methods:

• Localization of receptive fields using a thermal (warm) stimulus in an isolated splanchnic nerve-mesentery preparation.
• Recording impulse activity in response to controlled warming ramps and plateau phases.
• Application of bradykinin and von Frey hairs to assess chemical and mechanical sensitivity.
• Analysis of unit adaptation characteristics and sensitization to stimuli.

Main Results:

• Warm-sensitive receptive fields were identified and found to be densest near prevertebral ganglia and brown adipose tissue.
• Two types of warm-sensitive units were observed: slowly adapting (SA-W) and rapidly adapting (RA-W).
• A significant proportion of SA-W and RA-W units responded to bradykinin and/or mechanical stimuli, with some exhibiting transient sensitization to warming after bradykinin exposure.

Conclusions:

• Splanchnic thermosensitive neurons exhibit distinct response patterns to thermal, chemical, and mechanical stimuli.
• The observed characteristics and distribution suggest these neurons may contribute to cardiovascular adjustments during heat stress.
• Bradykinin can modulate the sensitivity of these thermosensitive units, indicating complex sensory integration within the splanchnic system.